The present invention relates to a gas turbine engine, principally for airplane propulsion purposes.
In the field of airplane engines, with increasing concerns over environmental pollution issues, large efforts are invested in finding solutions to decrease emissions from such engines.
Regarding stationary gas turbines, e.g. for power generation, a number of solutions have been provided for reducing emissions, including providing catalytic converters between different stages of the turbine, see for example U.S. Pat. No. 618,931 B1.
However, at full thrust operations in airplane propulsion applications, the solution of providing catalytic converters between different stages of the turbine could result in the maximum required cycle temperature damaging the catalytic converters. Such a solution would also introduce pressure losses in the flow between the turbines. Further, for airplane propulsion applications, such a solution would result in engine lengths that might be un-practical.
It is desirable to reduce emissions from a gas turbine engine.
It is desirable to reduce emissions from a gas turbine engine for airplane propulsion.
It is desirable to reduce NOx emissions from a gas turbine engine.
It is desirable to reduce emissions from a gas turbine engine for airplane propulsion, without reducing the thrust of the engine.
It is to reduce emissions from a gas turbine engine for airplane propulsion, without reducing the overall efficiency of the engine.
According to an aspect of the present invention, a gas turbine engine is provided comprising a first flow passage, and main combustion means in the first flow passage, characterized in that it comprises a second flow passage, and first catalytic combustion means in the second flow passage, wherein the second flow passage can communicate with the first flow passage at at least one upstream passage junction upstream of the main combustion means and upstream of the first catalytic combustion means, and the second flow passage can communicate with the first flow passage at at least one downstream passage junction downstream of the main combustion means and downstream of the first catalytic combustion means.
Thus, the first and second flow passages can be arranged as parallel flow passages extending from the upstream passage junction to the downstream passage junction. As understood in the art, air compressing means can be located upstream of the main combustion means, and a turbine assembly can be located downstream of the main combustion means and adapted to drive the air compressing means via at least one central shaft. The main combustion means can be adapted for traditional flame combustion, or, as described further below, it can comprise second catalytic combustion means.
The invention provides for the main combustion means being used for high thrust requirements, such as in take-off conditions in airplane propulsion applications. During the take-off of an airplane, the thrust requirements are larger than during cruise and descent. During operations requiring less thrust, the main combustion means can be allowed to work with reduced or shut-off fuel supply, whereby air is guided through the second flow passage. Thereby, the first catalytic combustion means can be used for oxidizing, as exemplified below, fuel for providing thrust, and thereby replace the main combustion means in such operations with lower thrust requirements. As explained closer below, since reactions occurring in catalytic combustion can take place at a temperature which is considerably lower than the temperature at which corresponding reactions take place in conventional flame combustion, it is possible, during use of the first catalytic combustion means, to considerably reduce emissions, specially the production of thermal nitrogen oxides (NOx). Thus, the main combustion means can provide at least the majority of the combustion process during the start phase of an airplane, and the first catalytic combustion means can provide at least the majority of the combustion process when thrust requirements are lower, such as during airplane cruise and descent.
Preferably, upstream flow control means are provided at the at least one upstream passage junction to control the communication between the first and second flow passages. Thereby, gas flow from the first flow passage to the second flow passage can be controlled. Also, preferably downstream flow control means are provided at the at least one downstream passage junction to control the communication between the first and second flow passages. Thereby, gas flow from the second flow passage to the first flow passage can be controlled.
Preferably, where air compressing means are provided in the first flow passage, upstream of the main combustion means, at least one of the at least one upstream passage junction is located downstream of at least a portion of the air compressing means. Thereby, upstream flow control means can be adapted to control communication at the at least one of the at least one upstream passage junction. As explained further below, in airplane propulsion applications, said upstream flow control means can be provided as bleed valves arranged to control the provision of compressed air to the first catalytic combustion means. Thereby, the first catalytic combustion means can participate in thrust generation during airplane start, take-off and climb. Also, in addition to the air being compressed for the combustion in the first catalytic combustion means, the air is heated, so as for it to quickly reach a temperature corresponding to the activation temperature of the first catalytic combustion means.
In some embodiments, where air compressing means are provided in the first flow passage, upstream of the main combustion means, and at least one of the at least one upstream passage junction is located downstream of at least a portion of the air compressing means, fuel injection means are arranged to provide fuel into the first flow passage upstream of the at least one of the at least one upstream passage junction. Thereby, it is possible to evaporate the fuel in the compressor so as to decrease the temperature of the compressed air.
In certain embodiments, for example in the one described below with reference to FIG. 7, where the air compressing means comprises a low pressure compressor and a high pressure compressor, at least one of the at least one upstream passage junction can be located downstream of the low pressure compressor and upstream of the high pressure compressor.
Preferably, where the engine is provided with air compressing means in the first flow passage, upstream of the main combustion means, at least one of the at least one upstream passage junction is located downstream of the air compressing means. Also, where the engine is provided with a turbine assembly in the first flow passage, downstream of the main combustion means, at least one of the at least one downstream passage junction is located upstream of the turbine assembly. Thereby, for example during cruise and descent in airplane propulsion applications, by controlling the gas to flow mainly through such an upstream passage junction located downstream of the air compressing means, and through such downstream passage junction is located upstream of the turbine assembly, essentially all air will be conducted through the second flow passage. Thereby, essentially all combustion will take place in the first catalytic combustion means, providing, as explained closer below, significantly reduced emission levels compared to traditional combustion.
Preferably, at least one of the at least one downstream passage junction is located downstream of at least a part of the turbine assembly. Preferably, where the turbine assembly comprises a high pressure turbine and a low pressure turbine, the at least one of the at least one downstream passage junction is located downstream of the high pressure turbine and upstream of the low pressure turbine. Thereby, where the low pressure turbine is linked to drive a low pressure compressor of the engine, the low pressure turbine can be driven by the first catalytic combustion means and in turn drive the low pressure compressor. As explained closer below, this provides an effective arrangement at the turbine during the participation of the first catalytic combustion means in thrust generation during airplane start, take-off and climb.
With said embodiment where the at least one of the at least one downstream passage junction is located downstream of the high pressure turbine and upstream of the low pressure turbine, it is possible to provide an inter-turbine combustion with the first catalytic combustion means. Compared to known gas turbine engines, this will increase the specific thrust of the engine for airplane propulsion. In other words, this will increase power efficiency, which in turn makes it possible to decrease the weight and size of the engine in view of a given thrust requirement. For airplane propulsion purposes, the decreased weight and size will decrease the weight and drag of the airplane configuration; in other words, it will give a more effective airplane/engine configuration.
In a special embodiment, exemplified below with reference to FIG. 6, the main combustion means comprises second catalytic combustion means.